Sudarsky and Volk, in a paper entitled "Aspherical Objective Lenses As an Aid in Indirect Ophthalmoscopy, A Preliminary Report," reported on their investigation of existing conoid lenses designed for subnormal vision when used as condensing lenses for indirect ophthalmoscopy. As a result of their investigation they recommended the use of three powers of conoid lenses for use in indirect ophthalmoscopy, the 15, 20, and 30 diopter lenses, each of the lenses having one aspheric surface, the other surface being plano or spherical. In use, the front aspherical surface faces the examiner.
In about 1969, Nikon of Japan introduced aspheric lenses for indirect ophthalmoscopy, with the front surface aspherical and the back surface spherical.
Other Japanese manufacturers, including Kowa and Topcon, introduced their aspheric lenses for indirect ophthalmoscopy late in the 1970 decade. These lenses likewise had an aspherical front surface and a spherical back surface. In the United States of America, American Optical Company and Younger Lens Company also manufactured and sold indirect ophthalmoscopy lenses with one surface aspherical and the opposite surface spherical.
Recently Zeiss of Germany introduced their indirect ophthalmoscopy lens with one surface aspherical and the opposite surface spherical.
In all of the above prior art indirect ophthalmoscopy lenses, only one of the two surfaces is aspheric. Although such aspherical indirect ophthalmoscopy lenses are a great improvement over spherical indirect ophthalmoscopy lenses, lens aberrations still remain so that as a condensing lens the light from the ophthalmoscope light source is not converged to a sharply defined image at the entrance pupil of the eye, and as an image forming lens, the aerial image of the fundus is curved away from the examiner and is increasingly astigmatic perpheralward.